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Diffstat (limited to 'Documentation/powerpc/syscall64-abi.rst')
| -rw-r--r-- | Documentation/powerpc/syscall64-abi.rst | 42 |
1 files changed, 30 insertions, 12 deletions
diff --git a/Documentation/powerpc/syscall64-abi.rst b/Documentation/powerpc/syscall64-abi.rst index e49f69f941b9..46caaadbb029 100644 --- a/Documentation/powerpc/syscall64-abi.rst +++ b/Documentation/powerpc/syscall64-abi.rst @@ -5,6 +5,15 @@ Power Architecture 64-bit Linux system call ABI syscall ======= +Invocation +---------- +The syscall is made with the sc instruction, and returns with execution +continuing at the instruction following the sc instruction. + +If PPC_FEATURE2_SCV appears in the AT_HWCAP2 ELF auxiliary vector, the +scv 0 instruction is an alternative that may provide better performance, +with some differences to calling sequence. + syscall calling sequence\ [1]_ matches the Power Architecture 64-bit ELF ABI specification C function calling sequence, including register preservation rules, with the following differences. @@ -12,16 +21,23 @@ rules, with the following differences. .. [1] Some syscalls (typically low-level management functions) may have different calling sequences (e.g., rt_sigreturn). -Parameters and return value ---------------------------- +Parameters +---------- The system call number is specified in r0. There is a maximum of 6 integer parameters to a syscall, passed in r3-r8. -Both a return value and a return error code are returned. cr0.SO is the return -error code, and r3 is the return value or error code. When cr0.SO is clear, -the syscall succeeded and r3 is the return value. When cr0.SO is set, the -syscall failed and r3 is the error code that generally corresponds to errno. +Return value +------------ +- For the sc instruction, both a value and an error condition are returned. + cr0.SO is the error condition, and r3 is the return value. When cr0.SO is + clear, the syscall succeeded and r3 is the return value. When cr0.SO is set, + the syscall failed and r3 is the error value (that normally corresponds to + errno). + +- For the scv 0 instruction, the return value indicates failure if it is + -4095..-1 (i.e., it is >= -MAX_ERRNO (-4095) as an unsigned comparison), + in which case the error value is the negated return value. Stack ----- @@ -34,22 +50,23 @@ Register preservation rules match the ELF ABI calling sequence with the following differences: =========== ============= ======================================== +--- For the sc instruction, differences with the ELF ABI --- r0 Volatile (System call number.) r3 Volatile (Parameter 1, and return value.) r4-r8 Volatile (Parameters 2-6.) -cr0 Volatile (cr0.SO is the return error condition) +cr0 Volatile (cr0.SO is the return error condition.) cr1, cr5-7 Nonvolatile lr Nonvolatile + +--- For the scv 0 instruction, differences with the ELF ABI --- +r0 Volatile (System call number.) +r3 Volatile (Parameter 1, and return value.) +r4-r8 Volatile (Parameters 2-6.) =========== ============= ======================================== All floating point and vector data registers as well as control and status registers are nonvolatile. -Invocation ----------- -The syscall is performed with the sc instruction, and returns with execution -continuing at the instruction following the sc instruction. - Transactional Memory -------------------- Syscall behavior can change if the processor is in transactional or suspended @@ -75,6 +92,7 @@ auxiliary vector. returning to the caller. This case is not well defined or supported, so this behavior should not be relied upon. +scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC. vsyscall ======== |